Hi Ade, if you need sub 16.5" stays + massive clearance for 2.5" then an e-stay is an option on a 29er, but i'd be concerned about BB flex. suspension bikes use suspension action to cope with a lot of the loads that would cuse twist and flex when riding a rigid e-stay. if you lock out an orange 5 or a meta 5 fully, they can feel pretty flexy all of a sudden, not just under pedalling but under cornering loads. they just don't tend to be ridden hard like that when locked.

E-stays in the old days often used hugely oversized alu and they still weren't ideal, the lack of triangulation does affect things, but also i think we moved on after realising that sub-16" stays weren't so important after all.

if i was looking at making a 2.5" - 3" rear tyre 29er (we did at one point, a snow 26" / 29er convertable idea) then the best solution is to ignore conventional 50mm chainlines and work with DH kit ie wider BB shells / hubs. Dr Jon's Vertigo is an interesting bike along those lines and a few US builders are seeing the opportunities that wider chainlines present.

I wonder how a really well-caked with mud 2.5" 29er tyre would feel? slow. heavy. ok for a smi-fat snow bike, but with such a big contact patch my exp with 29ers is that you can go skinnier / lighter and get away with it.

i'm not saying i'm right or that e-stays are wrong, just my 2p on it. i'm really interested to see your bike, could be very cool! have you seen Bystickle's customs? similar to the Vertigo bike in some areas.

For the Singular Pegasus riders early in this thread: what sort of frame bags are you using on your bike

Bit late picking this up - mine is home made, and is the beginning of a small cottage industry for my better half under the name of Wildcat Gear. A bit more here, but more to follow on the forum in due course.